In common mercury vapor fluorescent lamps, the enclosed mercury vapor is stimulated to emit invisible ultraviolet light that in turn excites a phosphor coating on the lamp wall. The stimulated phosphor then emits the visible light. Mercury based fluorescent lamps do not work well in cold environments. The available mercury vapor existing at normal temperatures is progressively reduced with lower temperature. FIG. 1 shows the lumen output of a fluorescent lamp operated at different temperatures. There is about a 62 percent drop in light output from 25.degree. C. (77.degree. F.) to 13.9.degree. C. (57.degree. F.), and a 92 percent drop from 25.degree. C. (77.degree. F. ) to -31.1.degree. C. (-24.degree. F.). Light output is then so variable over normal temperatures that ordinary mercury fluorescent lamps are not normally used outside. Otherwise, fluorescent lamps are well know to be efficient, and long lived. There has been a long need for a fluorescent type lamp that can operate in cold environments.
Mercury free, rare gas, fluorescent lamps have been attempted in the past. Argon, krypton, and xenon lamps have been operated with phosphors, under a variety of conditions. For neon, it was known that if the lamp was operated at less than 5 Torr, the gas atoms had sufficient time between collisions to emit ultraviolet light to stimulate a phosphor. Unfortunately, at such low pressures, the phosphor disintegrates, and the electrodes rapidly sputter. As a result, while a lamp may start, it has a short life. At higher pressures, and operated in the usual way, ultraviolet emission was quenched.
Neon lamps are known to produce red light, and therefore offer the opportunity of an unfiltered vehicle stop lamp. There are however problems to be overcome. Typical neon sign lamps use long tubes about one or two centimeters in diameter, that contain the diffused gaseous neon plasma light source. These lamps typically have inputs from 1100 to 1200 volts, at a few milliamps of power. These lamps give off a diffuse, low intense light. For proper visibility, light must be reflected and focused to concentrate it down the road, but a diffuse light source with a diameter of one or two centimeters cannot be efficiently reflected or focused. There is then a need for a small diameter, high intensity, neon stop lamp.
Vehicle tail lamps commonly include red stop lamps, and a separate amber signal lamps. The SAE (Society of Automotive Engineers) has determined a particular amber and a particular red that are preferred for signal, stop, and warning illumination. These values are usually achieved with a tungsten filament lamp whose white light is filtered to provide the proper color. Tungsten lamps are not efficient when operated in this manner. Tungsten lamps have limited lives, and relatively slow turn on times. Tungsten lamps also become dimmer as they age. Tungsten lamps do however provide an intense source that can be reflected and focused.
Typical neon sign lamps having a mercury component, are too orange to satisfy the SAE requirement, so there is a need for a neon lamp whose color meets the SAE chromaticity requirements. Typical neon and other gas discharge lamps include mercury for starting, but these mercury dosed, neon lamps are also affected by cold. There is then a need for a mercury free neon lamp that meets SAE color requirements.
Some rare gases, argon, xenon, and krypton are known to emit ultraviolet light so as to stimulate a phosphor. Neon has a higher first energy band than other rare gases, so when the other rare gases, in concentrations higher than about one percent, are mixed with neon, the spectral output is substantially the result of the other, more easily emitting gases. Nonetheless, neon is used in such mixtures, usually to inhibit sputtering of the electrode.
Two separate lamp housings are used for the red and amber vehicle lamps, even though the amber signal lamp is normally not on most of the time. It would be useful if the one lamp housing could contain both the red and amber lamps.
Examples of the prior art are shown in the following U.S. patents:
U.S. Pat. No. 2,123,709 issued to L. J. Bristow et al on Jul. 12, 1938 for a Therapeutic Light Ray Apparatus shows narrow, folded over neon tube for therapeutically probing body cavities.
U.S. Pat. No. 2,152,999 issued to C. J. Milner for Gaseous Electric Discharge Lamp Device shows a lamp with 1 to 10 millimeters of neon pressure in an inner capsule along with cadmium in the fill. An outer silver layer reflects heat and visible light back into the inner capsule. The emitted ultraviolet light excites a phosphor to visible light emission. The power source is identified as an alternating current source, but is not specified further.
U.S. Pat. No. 2,421,571 issued to W. E. Leyson for Fluorescent Glow Lamp on Jul. 25, 1945 shows a glow lamp with a neon pressure of about 35 millimeter's pressure. The fill is 95 to 99% neon, and the rest krypton. Alternatively a mixture of 20 to 30 percent krypton and the rest argon is used. A variety of phosphors are used on the inner wall to produce visible light in different colors.
U.S. Pat. No. 2,874,324 issued to G. F. Klepp et al on Feb. 17, 1959 for Electric Gaseous Discharge Tubes shows a neon discharge device having a pressure of about 25 millimeters of mercury. By choosing the envelope size and lamp pressure, the voltage regulation of the device can be optimized to offset temperature induced response variations in the device.
U.S. Pat. No. 3,536,945 issued to C. D. Skirvin for Luminescent Gas Tube Including a Gas Permeated Phosphor Coating shows a neon and krypton gas filled lamp. No mercury is used in most examples. A phosphor is used to convert ultraviolet light to visible light. The gas combination is driven by an alternating current with a 23 kilohertz frequency. The gas combination enables the neon to act as a starter, while the krypton radiates at the steady state frequencies of excitation. The claim specifically states that neon and krypton alone do not produce ultraviolet light, and therefore the two must be combined. Other gas mixtures are used, all at pressures of from about 5 to 10 millimeters mercury.
U.S. Pat. No. 3,778,662 issued to P. D. Johnson for High Intensity fluorescent Lamp Radiating Ionic Radiation within The Range of 1,600-2,300 A.U. on Dec. 11, 1973 shows a fluorescent lamp using a rare gas and vaporizable fill.
U.S. Pat. No. 4,039,889 issued to Egon Vicai for Blue-White Glow Lamp on Aug. 2, 1977 shows a glow lap with from 1 to 15 percent xenon and 85 to 99 percent neon. A phosphor is coated on the inside of the envelope. The fill pressure is from about 50 to 112 Torr. The lamp is operated at about 40 to 70 volts direct current.
U.S. Pat. No. 4,196,374 issued to Harald Witting for Compact Fluorescent Lamp and Method of Making on Apr. 1, 1980 shows a compact fluorescent lamp using a "high percentage of neon" as a gas fill. The specification is generally directed to the glass shaping and manufacture, and is silent as to mercury. It is not clear whether mercury is included or not.
U.S. Pat. No. 4,461,981 issued to Saikatsu for Low Pressure Inert Gas Discharge Device shows a neon lamp at a pressure of less than 15 Torr, operated at more than 5 kHz. There is no phosphor used in the lamp.
U.S. Pat. No. 4,792,727 issued to Valery A. Godyak on Dec. 20, 1988 for a System and Method for Operating a Discharge Lamp to Obtain Positive Volt-Ampere Characteristic shows a gas discharge lamp operated with a base electron heating current, and an additional pulsed ionization current occurring faster than the diffusion time of the gas, said to be typically about 1 microsecond. A driving wave with a frequency of 3333 Hertz and a pulse width of 1 microsecond is suggested. A lamp is operated at 264 milliamps.
U.S. Pat. No. 4,882,520 issued to Tsunekawa for Rare Gas Arc Lamp having Hot Cathode on Nov. 2, 1989 shows a 6 millimeter inside tube diameter tube coated with a phosphor. The tube is filled with xenon from 20 to 200 Torr. The electrodes are hot cathode types. Neon is suggested as an alternative fill gas. The patent does not disclose cold electrode operation, nor is there any consideration of pulsed mode operation.
U.S. Pat. No. 4,914,347 issued to Osawa for Hot Cathode Discharge Fluorescent Lamp Filled with Low Pressure Rare Gas shows a narrow tube filled with a mixture of xenon and neon. A Hot cathode and a fluorescent coating are used. The pressure is less than 10 Torr. Including neon was found to help preserve the phosphor coating.
U.S. Pat. No. 4,926,095 issued to Shinoda for Three Component Gas Mixture for Fluorescent Gas Discharge Color Display Panel shows a flat panel display using xenon, neon and argon as a gas fill to stimulate phosphors on a panel display.
U.S. Pat. No. 5,034,661 issued to Sakurai for Rare Gas Discharge Fluorescent Lamp Device on Jul. 23, 1991 shows a rare gas, fluorescent lamp with a pulsed power source. The pulsing is from 4 to 200 kHz. The lamp pressure is from 10 to 200 Torr. The gas fill is a rare gas, but xenon, and krypton are the ones mentioned.
U.S. Pat. No. 5,072,155 issued to Takehiko Sakurai et al. on Dec. 10, 1992 for Rare Gas Discharge Fluorescent Lamp Device discloses a copying machine lamp with high brightness and efficiency. Sakuria suggests a xenon, argon, or krypton gas filled lamp, the use of a pulsed power supply where the pulse period is less than 150 microseconds, and the cycle period is greater than 5% of the pulse to avoid sputtering deterioration of the electrodes, and less than 70% of the pulse period to maximize light output for energy input. The gases emit ultraviolet light that stimulates a fluorescent coating to produce visible light.
U.S. Pat. No. 5,043,627 issued to L. Fox for High-Frequency Fluorescent Lamp shows a rare gas lamp with a phosphor coating. The lamp is driven by two cold cathodes operated at high frequency (10 to 50 kHz) radiators. The preferred gas fill is argon, but others are mentioned.
Canadian Patent Application 2092383 for Low Pressure Discharge Lamp and Luminare Provided with Such a Lamp by Bauke J. Roelevink et al and assigned to Philips Electronics N.V. shows a tubular glass vessel filled with a rare gas. Where mercury or xenon are present, a fluorescent coating may be applied. The lamp inside diameter is from 1.5 to 7 millimeters. These lamps are described as filled with various rare gases and rare gas and mercury fills. Pressures used ranged from 30 to 160 millibar (39.9 Torr to 213.3 Torr), depending on the fill type. Phosphors were used to coat some of the mercury or xenon containing lamps, and neon was used at a pressure of 15 millibar (19.99 Torr). No neon lamp is actually disclosed with a phosphor coating, nor is neon used at a pressure above 19.99 Torr. In general, Roelevink concerns a seal structure using a metal tube sealed through the envelope to a second glass vessel, presumably to thermally separate the final seal section.
Disclosure of the Invention
A neon lamp that may generate amber light or red light may be operated the neon discharge lamp has an enclosed, substantially pure neon fill with a pressure not less than 20 Torr, the lamp having a phosphor that is responsive to radiation by neon stimulated to a particular energy level, the phosphor being positioned to be within responsive range of the neon emission comprising supplying electric energy with a first energy pattern to cause the neon fill to emit light in a first wavelength region with a first chromaticity, and causing the neon gas additionally to stimulate the phosphor to emit light in a second wavelength region with a second chromaticity, and combining the first chromaticity light and the second chromaticity light to give a light with a third chromaticity.